The present invention relates to an ultrasonic testing apparatus and method thereof that are suitable for shortening time taken to inspect turbine forks.
To facilitate the manufacturing and maintenance of a turbine used in a power generating plant, its rotor and turbine blades are manufactured separately, and the structural portions of the forks of the turbine blades are inserted to the disc on the rotor and fixed by inserting pins into holes formed in the forks, as shown in FIGS. 15A and 15B. As the turbine rotates, stress is generated to the fork holes, generating cracks at locations as shown in FIG. 15C.
In conventional inspection for cracks in the fork holes, the turbine blades are taken off and magnetic particle testing (hereinafter referred to as MT) is then performed.
The MT is a method for detecting a leak of a magnetic flux from a defect when a magnetic field is applied to a test object as illustrated in FIG. 16. Ultraviolet rays are irradiated to magnetic metal particles on which a fluorescent material is applied, the fluorescent material being accumulated by the magnetic flux that leaks from the defect. Whether the magnetic metal particles is accumulated can be determined by observing whether there is fluorescent light, and thus whether there is a defect can be determined. In inspection for fork hole defects based on the MT, since it is necessary to pull out pins and to separate the turbine blades from the disc, it is a problem that time of the inspection lengthens.
Accordingly, in fork hole inspection, there is an approach to ultrasonic testing (hereinafter referred to as UT). The UT is a method for sending an ultrasonic wave to a test object and receiving a reflected wave. Whether there is a defect can be determined on the basis of whether there is the reflected wave from the defect. If a UT sensor is placed at the root of the blade to make an ultrasonic wave directly incident to a place of a defect as shown in FIG. 17A, a spacing is left between the fork and the UT sensor because the location at which the sensor is placed is curved. As a result, it becomes difficult to make an ultrasonic wave incident. If the UT sensor may be placed on a side surface of a fork as shown in FIG. 17B so that an ultrasonic wave reflects in the fork and the reflected ultrasonic wave is incident to a place of a defect, it is difficult to locate a place of a testing because the incident path of the ultrasonic wave is not clear. Therefore, the UT inspection is not used in practical applications. Japanese Patent Laid-open No. 2002-310998 discloses ultrasonic testing technology applied to embedded parts that are not fork-shaped.